This invention relates to an umbrella mechanism.
According to the invention there is provided an umbrella mechanism comprising
a central post having an upper end and a lower end;
a plurality of ribs surrounding the post that are hingedly connected to the upper end of the post, the ribs being displaceable between a collapsed condition wherein the ribs are disposed adjacent the post and an open condition wherein the ribs extend radially from the post;
a sliding hub that is slideably retained on the post;
a plurality of struts surrounding the post and having post ends that are hingedly connected to the hub and rib ends that are hingedly connected to the ribs;
at least one tensioning element that is attached to the ribs; and
urging means that exerts a pulling force on the tensioning element in a direction for causing elevation of the ribs into the open condition thereof.
The umbrella mechanism may include a plurality of flexible slender tensioning elements that each extend from an operative upper end of the urging means to a distal end of a different one of the ribs, where the slender element is attached to the rib.
The urging means may be in the form of a gas spring that is disposed at the upper end of the central post and that acts between the post and the tensioning elements for exerting said pulling force on the tensioning elements.
The umbrella mechanism may include a cap that is mounted to an operative upper end of the gas spring and that defines a radially extending flange formation from which the tensioning elements extend, the flange formation being sufficiently wide so as to space the tensioning elements from the central post a sufficient distance to prevent interference between the tensioning elements and upper ends of the ribs when the ribs are in their collapsed condition.
Each strut may define a longitudinal axis along its length and the central post defines a longitudinal axis along its length, the struts each forming an angle defined between the longitudinal axes of the strut and the central post, in an optimum range between 70 and 75 degrees, when the ribs are disposed in their open condition.
The gas spring may project above the upper end of the central post in an arrangement wherein the gas spring projects progressively further above the upper end of the central post as the ribs are displaced into their open condition, thereby increasing the lever arm between the tensioning elements and the ribs, thus assisting in holding the ribs in their open condition.
The central post may comprise a post section having a lower end defining said lower end of the post and an upper end; and an extension section that has a lower end and an upper end that defines said upper end of the central post to which the ribs are hingedly connected, the extension section being mounted to the post section at an upper end region thereof in an arrangement wherein the extension section is telescopically displaceable with respect to the post section, thereby permitting lifting of the extension section with respect to the post section so as to allow lifting of the ribs clear of obstacles that may be in the way of the ribs when the ribs are displaced between their open and collapsed conditions.
The extension section may define an open-topped hollow section within which a lower end region of the gas spring is located, the extension section defining a stop formation against which a lower end of the gas spring abuts.
The post section may have a stop formation at a predetermined position along its length, that is spaced above a position that would otherwise be the lowest point of travel of the sliding hub when the ribs are in their collapsed condition, thereby causing the sliding hub to abut against the stop formation when the ribs are being displaced into their collapsed condition, in use, and the extension section to be displaced telescopically upwardly with respect to the post section, thereby lifting the ribs in the process, until the ribs are finally in their collapsed condition.
The tensioning element may be in the form of a flexible sheet element having a peripheral edge region that is attached to the ribs at their distal ends, with the urging means exerting a force on a central region of the sheet element for pushing the sheet element upwards for exerting a pulling force on the sheet element for lifting the ribs.